A hydrotreating catalyst may be defined as any catalyst composition which may be employed to catalyze the hydrogenation of hydrocarbon feedstocks. Such catalyst compositions are well known to those of ordinary skill in the art and several are commercially available. Metal oxide catalysts which come within this definition include cobalt-molybdenum, nickel-tungsten, and nickel-molybdenum. Typical supports for hydrotreating metal oxide catalysts include alumina, silica and silica-alumina supports.
In the past, ex-situ methods of presulfiding supported metal oxide catalysts have suffered from excessive stripping of sulfur upon start-up of a hydrotreating reactor. As a result of sulfur stripping, an increase in the product weight percent of sulfur is observed along with a decrease in catalyst activity.
The use of high boiling oils and hydrocarbon solvents to aid the incorporation of sulfur into a catalyst is not believed to have been previously taught by prior presulfiding methods. Hereforth, a high boiling oil is defined as an oil whose initial boiling point is greater than 400.degree. F.
Hydrotreating catalysts are typically presulfided by incorporating sulfur compounds into the porous catalyst prior to hydrotreating a hydrocarbon feedstock. For example, U.S. Pat. No. 4,530,917 to Berrebi discloses a method of presulfiding a hydrotreating catalyst with organic polysulfides.
U.S. Pat. No. 4,177,136 to Herrington et al discloses a method of catalyst presulfiding wherein a catalyst is treated with elemental sulfur. Hydrogen is then used as a reducing agent to convert the elemental sulfur to H.sub.2 S in situ. Problems arise, however, upon start-up of a reactor due to excessive sulfur stripping.
U.S. Pat. No. 4,089,930 to Kittrell et al discloses the pretreatment of a catalyst with elemental sulfur in the presence of hydrogen.